Lenz’s law: The direction of induced emf due to the process of electromagnetic induction is such that, it always sets up a current to oppose the basic cause responsible for inducing the emf.
The mathematical representation is, e = - N (dΦ/dt)
Explanation: If a bar magnet with its N pole facing the coil is brought close to the coil, due to the relative motion between the coil and the magnet, there is a change in flux linkage with the coil. An emf is induced in the coil and current I starts flowing. This current produces its own magnetic field The direction of this current is such that it produces an N Pole on the side of the coil it faces. As N-pole produced by the coil is close to the N pole of magnet, there is a force of repulsion between the two and this will oppose the magnet coming closer to the coil. Thus the induced emf produces current in such way that it opposes the cause behind its own production.